802.1Q-2014 I-Tag and MAC addresses

I am reading IEEE 802.1Q-2014 for interest. This incorporates I-Tags, which define backbone service instances. In a few places, the standard implies or states that the I-Tag includes the C-DA and C-SA. For example, Clause 26.2 PBBN example: "During de-encapsulation, the B-DA, B-SA, B-TAG, and I-TAG are stripped. The C-DA and C-SA from the I-TAG will become the DA and SA transmitted to the receiving C LAN." Whereas my understanding is that the I-Tag is part of the encapsulation, and the C-DA and C-SA are part of the encapsulated frame. Figure 25-6 "Encapsulated service frames at ISS" is also unclear to me. Am I misunderstanding something? Are they really considered part of the I-Tag, or are they part of the following (encapsulated) frame?

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